DE102018217526A1 - Method for determining a parameter of a machining process and machine tool - Google Patents

Abstract

The invention relates to a method for determining at least one parameter (α, γ, P, R) for the process quality in a machining process, in particular in a laser cutting process, comprising: in particular cutting machining of a workpiece (8) while moving a machining tool, in particular a laser machining head, and the workpiece (8) relative to one another, monitoring an area (26) on the workpiece (8), which preferably comprises an interaction area of the processing tool, in particular the laser processing head, with the workpiece (8), and determining at least one parameter (α, γ, P, R) for the process quality based on the monitored area (26). The method is characterized by determining at least one position-dependent parameter for the process quality on the basis of a plurality of measured values of the at least one parameter (a) at the same processing position (B) and / or at least one direction-dependent parameter for the process quality on the basis of a plurality of measured values of the at least one parameter (a) in the same machining direction (B), in particular in the same machining direction (B) at one and the same machining position (B). The invention also relates to an associated processing machine (1).

Description

The present invention relates to a method for determining at least one parameter for the process quality in a machining process, in particular in a laser cutting process, comprising: in particular cutting machining of a workpiece while moving a machining tool, in particular a laser machining head, and the workpiece relative to one another, monitoring an area on the Workpiece, which preferably comprises an interaction area of the machining tool with the workpiece, and determining at least one parameter for the process quality on the basis of the monitored area. The invention also relates to a processing machine comprising: a processing tool for in particular cutting processing of a workpiece, a movement device for moving the processing tool and the workpiece relative to one another, a monitoring device for monitoring an area on the workpiece, which preferably comprises an interaction area of the processing tool with the workpiece , and an evaluation device that is configured to determine at least one parameter for the process quality based on the monitored area.

Such a method and a corresponding device are, for example, from the WO2012107331A1 known. It describes, among other things, that a cutting front angle of a laser cutting process can be determined as a parameter for the process quality.

Also from the WO2015036140A1 A method and a device are known in which the cutting front angle of a kerf formed in a laser cutting process is determined as a characteristic parameter of the cutting process on the basis of the detected interaction area. The cutting front angle represents a parameter for the process quality or for the process robustness, especially when flame cutting.

In the WO2018069291A1 A method and a device are described in which at least one measurement variable for the course of the gap width of a kerf in the thickness direction of the workpiece, in particular for an angle between the two cutting edges of the kerf, is determined on the basis of at least one image of an area of the workpiece to be monitored. The (opening) angle between the two cutting edges of the kerf represents a parameter for the process quality or for the process robustness, especially when fusion cutting.

In the DE102005022095A1 describes a method and a device for determining a lateral relative movement between a machining head and a workpiece during machining of the workpiece. In the method, the surface of the workpiece in the region of the machining head is illuminated with optical radiation, and optical radiation reflected from the surface of the workpiece is repeatedly detected with an optical detector in order to obtain optical reflection patterns of the surface of the workpiece at different times. The lateral relative movement is determined by comparing the successive reflection patterns.

From the EP3159093A1 describes a method for controlling laser cutting processes in the high-performance range with cutting process interruption and a corresponding method. In the method, at least a partial route of a processing route cut in the course of a first partial processing operation is scanned and at least one quality feature of the processing process is determined on the basis of the scan result and compared with predefined quality specifications. An online process monitoring method can additionally be carried out at least temporarily for the cutting process, with at least one monitoring parameter of an online monitoring parameter set being adapted depending on the result of the comparison.

In the DE 102011079083A1 describes a method for machining a workpiece, in which a surface topography of the workpiece to be machined is recorded at least in sections and a minimum desired distance of the machining head from the workpiece is determined on the basis of the previously recorded surface topography.

From the EP1497851 it is known for laser cutting a substrate to measure the laser energy density in a focal plane using a power measuring device in a position-dependent manner and to use the measured values to regulate the pulse energy and / or the pulse repetition rate for a constant laser energy density at scanned points in a field of view on the substrate to care. The laser is controlled by a machine-specific "laser cutting strategy file".

Object of the invention

The invention is based on the object of providing a method and a processing machine in which at least one parameter of a processing process is determined in order to identify faults in a processing machine used for the processing.

Subject of the invention

This object is achieved according to the invention by a method of the type mentioned at the outset, which is characterized by the steps: determining at least one position-dependent parameter for the process quality on the basis of a plurality of measured values of the at least one parameter at the same processing position and / or at least one direction-dependent parameter for the process quality on the basis of a plurality of measured values of the at least one parameter in the same machining direction, in particular in the same machining direction at one and the same machining position. For the purposes of this application, the term process quality also means process robustness, i.e. both terms are used synonymously. In the context of this application, a parameter for the process quality is also understood to mean a parameter that influences the process quality.

Surface processing machines in particular, for example 2D laser cutting machines, can have direction and / or position-dependent faults which influence the process result or the process quality. Such disturbances are typically only dependent on the machining position or the machining direction, but essentially independently of the geometry of the contour to be cut, the type of machining process (e.g. flame cutting or fusion cutting) and the machining parameters. In the sense of this application, a fault is also understood to mean a deviation from a reference state.

For example, position-dependent disturbances can occur on (support) webs arranged in the work area and direction-dependent disturbances can be due to polarization and / or caustic inhomogeneities of the laser beam, to inhomogeneities of the gas stream or gas pressure of a gas stream emerging from a nozzle during processing (e.g. due to damage of the nozzle or due to an incompletely symmetrical construction of the machining head which supplies the gas to the nozzle) can be attributed to material anisotropy, etc. With the aid of the method described above, it is possible to identify or localize such direction and / or position-dependent faults. For this purpose, it is necessary to eliminate deviations that also occur, which are caused by disturbances that are not position- or direction-dependent, by a sufficient number of measured values of the parameter, so that a (essentially exclusively) position- or direction-dependent parameter is formed. The number of measured values of the parameter that are required for the elimination depends on how significant the direction and / or position-dependent disturbance is. The number of measured values can range from three measured values (in extreme cases) to several hundred measured values if the position and / or directional dependence of the disturbance is comparatively small. For example, in the case of a direction-dependent disturbance caused by a slightly inhomogeneous beam caustics of the laser beam, a high number of measured values may be required, while in the case of an optical signal from a laser cutting sensor system, which is detected when a support web is passed over, a small number of measured values of the parameter is required in order to obtain the Eliminate contribution from non-positional disturbances.

In the sense of this application, a direction-dependent parameter is understood to mean a parameter which is dependent on the machining direction and which is parameterized, for example, by an angle (between 0 ° and 360 °). The at least one direction-dependent parameter can possibly be determined independently of the respective processing position, i.e. This is not differentiated according to the machining position, but rather measured values at machining positions from the entire machining field are used to determine the direction-dependent parameter. As a rule, however, the direction-dependent parameter is determined at a respective processing position, i.e. the measured values that are used to determine the direction-dependent parameter are all measured at the same processing position.

In one variant, a statistical analysis of the plurality of measured values is carried out to determine the position-dependent parameter and / or the direction-dependent parameter for the process quality. In the simplest case, the position-dependent or direction-dependent parameter can form the average of the measured values determined at the respective machining position or in the respective machining direction. However, it goes without saying that the mean value does not always represent a suitable measure for determining the position-dependent or direction-dependent parameter from the plurality of measured values, but that another statistical measure is used to eliminate non-direction-dependent or position-dependent disturbances , for example the median, or more complex statistical evaluations can be carried out.

In a further variant, the parameter is recorded continuously during a machining process, for example by means of a sensor or a monitoring device, and a currently determined measured value of the parameter is assigned to a respective machining position and / or a respective machining direction. For monitoring process quality during the Machining is typically continuously monitored at least one parameter for the process quality, for example, to be able to intervene instantly in the machining process. The determination of the parameter during the machining process takes place along a predetermined path curve, which corresponds to the cutting contour in a laser cutting process and which is known to the machine control. The parameter determined at a specific point in time can therefore be assigned to a processing position and a (current) processing direction. If necessary, the current machining direction and possibly also the machining position can also be detected by a sensor or a monitoring device, as is the case, for example, for the machining direction or the lateral relative movement between the machining tool and the workpiece in the one cited at the beginning DE102005022095A1 is described. It goes without saying that the processing position or the processing direction is typically assigned to the continuously recorded characteristic variable with a predetermined discretization, ie with a predetermined grid dimension.

In a further variant, machining positions are determined on the basis of the position-dependent parameter, which form at least one fault position range during machining, and / or machining directions are determined on the basis of the direction-dependent parameter, which form at least one fault angle range during machining. By frequently measuring at the same processing position or in the same processing direction, preferred positions and preferred angles or interference positions and interference angles can be identified. The identification of the interference positions or the interference angle can also be carried out using statistical methods on the basis of the position-dependent or direction-dependent parameter. In the simplest case, the interference position ranges or the interference angle ranges are determined on the basis of a comparison of the position-dependent or direction-dependent parameter with a threshold value; Processing positions or directions at which the parameter exceeds or falls below the threshold value are identified as fault position ranges or as fault angle ranges.

For example, in the case of laser processing machines, preferred or interference angle ranges can be determined, the cause of which is, for example, in the processing beam (polarization, caustic inhomogeneity, angle of incidence, etc.), in the movement devices or drives used for the movement of the processing tool and / or the workpiece (transverse and / or longitudinal vibrations) or e.g. lie in the material of the workpiece (anisotropy, rolling direction).

Correspondingly, fault position ranges can be determined, which depend on the machining position or on the position in the work area and which are caused, for example, in the laser beam guidance (in particular in the case of a CO ₂ laser), in the mechanical suspension of the machining tool, for example in the form of a laser machining head ( e.g. unfavorable moments in the case of cantilevered supports, gear wheel play, mechanical tolerances, etc.), the mechanical mounting of the workpiece (sheet metal), e.g. a pallet vibration, poor or too few support ridges, the support points of the supports (potential defects when the support point is exceeded, Process influence by slagged webs) or the workpiece or sheet properties (thinning in the edge area, dirty areas).

In one variant, machining positions and / or machining directions are determined during the movement of the machining tool and the workpiece relative to one another as a function of the determined position-dependent characteristic variable, in particular the fault position range, and / or on the basis of the direction-dependent characteristic variable, in particular the fault angle range. The knowledge of areas and / or directions with particularly good or particularly bad process properties can be used to avoid interference position ranges or interference angle ranges during machining, for example by suitable nesting or arrangement of the cutting contours of the workpiece parts to be cut free from the workpiece , ie can be realized by a suitable process planning of the machining process. It goes without saying that targeted fault diagnosis can also be carried out, i.e. a targeted check of the causes of the disturbance (s) can be carried out at a respective fault position range or at a respective fault angle range. Both fault diagnosis and optimization of work planning, i.e. the avoidance of the critical interference position ranges or the interference angle ranges can be carried out fully automatically without the intervention of an operator.

In a further variant, the plurality of measured values of the at least one parameter is determined in several machining processes on the same machine tool and / or the position-dependent parameter and / or the direction-dependent parameter is / are determined on several machine tools of identical construction. In the first case, position- or direction-dependent parameters are determined on a specific processing machine in order to identify errors, in the second case, position- or direction-dependent parameters are determined on several identical processing machines. By comparing between The polarization- or direction-dependent parameters that were determined on several identical processing machines can eliminate the influence of the individual processing machine and systematic weaknesses in the machine design of a particular type of processing machine can be identified.

In a further development, the plurality of measured values of the at least one characteristic variable is determined in several machining processes on the same processing machine, and a change in the measured values over time is taken into account when determining the position-dependent characteristic variable and / or the direction-dependent characteristic variable. The measured values of the at least one parameter, which are determined in successive machining processes on one and the same machine tool, can be subject to a change over time. If the parameter for which the measured values are determined is, for example, a focal position in the beam direction of the laser beam, this can change over time, for example, due to contamination of a processing optics, since this can lead to a so-called thermal lens that changes the focus position. In the event that a statistically significant change in the measured values over time is determined, this change can be taken into account when determining the parameter.

In general, it is possible to take into account the change in the measured values over time in that older measured values are less weighted when determining the parameter than measured values that were determined during machining processes that were not so long ago. Measured values that were determined in the case of machining processes that were carried out very long ago may also no longer be taken into account when determining the characteristic variable. In particular, these measured values can be discarded or deleted if necessary.

In a further variant, the method comprises storing the determined position-dependent parameter and / or the fault position range and / or the determined direction-dependent parameter and / or the fault direction range in a data memory. In the data storage, for example in the machine control, on a central computer or in the cloud, data about the fault position area (s) or the fault position direction (s) are collected. In particular, the position-dependent (n) or angle-dependent (n) parameter (s) or the fault position or angle range (s) of several processing machines that are operated at different locations can be brought together in the data memory.

In one variant, the parameter is selected from the group comprising: cutting front angle of a cutting front of a kerf and opening angle between two cutting edges of the kerf. The cutting front angle represents a parameter for the process quality, in particular in the case of flame cutting, and can, for example, refer to the one cited in the introduction WO2012107331A1 or to the ones quoted in the introduction WO2015036140A1 described manner can be determined. The decrease in the width of the kerf of the cutting gap in the thickness direction of the workpiece, which can be determined, for example, by the opening angle between the cutting edges of the kerf or by a measurement variable indicative of this (cf. WO2018069291A1 ) represents a parameter for the process quality and the process robustness in fusion cutting.

In a further variant, the parameter is selected from the group comprising: positioning accuracy and directional accuracy when moving the processing tool and the workpiece relative to one another. The positioning or directional accuracy also has an influence on the process quality and depends on the machining position or the machining direction due to the suspension of the machining tool or the mounting of the workpiece. The directional accuracy during processing can be done, for example, with the help of the one cited in the introduction DE102005022095A1 described method can be determined, which describes the lateral relative movement between the machining tool and workpiece. The directional accuracy of the relative movement at a respective processing position can be determined by a comparison with the target processing direction, which results from the path planning. Accordingly, the current machining position can also be determined using a suitable sensor or a suitable monitoring device and compared with the target machining position resulting from the path planning in order to determine the position accuracy.

Another aspect of the invention relates to a processing machine of the type mentioned at the outset, in which the evaluation device is configured or programmed, at least one position-dependent parameter for the process quality based on a plurality of measured values of the at least one parameter at the same processing position and / or at least one direction-dependent parameter for to determine the process quality on the basis of a plurality of measured values of the at least one parameter along the same machining direction, in particular along the same machining direction at one and the same machining position. As described above in connection with the method, the Processing machine can be determined on the basis of the position and / or direction-dependent characteristic variable, position and / or direction-dependent disturbances. The processing machine can in particular be a so-called 2D laser cutting machine, in which the workpiece typically rests on a workpiece support and the processing tool is moved in the form of a laser processing head in a lateral direction over the workpiece.

In one embodiment, the evaluation device is configured or programmed to carry out a statistical analysis of the plurality of measured values in order to determine the position-dependent parameter and / or the direction-dependent parameter for the process quality. As described above, a statistical analysis or evaluation of the measured values can be used to eliminate influences on the process quality that are not dependent on the processing position and / or on the processing direction.

In a further embodiment, the monitoring device is designed to continuously monitor the at least one parameter and the evaluation device is designed to assign a currently determined measured value to the parameter to a respective machining position and / or a respective machining direction. The evaluation device can be provided in the processing tool, but can also form part of a control device of the processing machine.

In a further embodiment, the evaluation device is configured or programmed to use the position-dependent parameter to determine machining positions that form at least one fault position range during machining and / or to use the direction-dependent parameter to determine machining directions that form at least one fault angle range during machining. With regard to this embodiment, reference is made to the above statements in connection with the method.

In a further embodiment, the processing machine comprises a control device for controlling the movement of the processing tool and the workpiece relative to one another, which is preferably configured, processing positions and / or processing directions for the movement of the processing tool and the workpiece relative to one another as a function of the determined position-dependent characteristic variable, in particular of the interference position range, and / or on the basis of the direction-dependent parameter, in particular of the interference angle range. As was described further above, the fault position ranges or the fault angle ranges can be taken into account in the work planning or in the sheet metal layout plan, in order to avoid these as far as possible during the machining process.

In one embodiment, the monitoring device and the evaluation device are configured, based on the monitored area as a parameter for the process quality, a cutting front angle of a cutting front of a kerf, an opening angle between two cutting edges of the kerf, a positioning accuracy and / or a directional accuracy when moving the processing tool and the like Determine workpiece relative to each other. The parameter which describes the positioning accuracy and / or directional accuracy in the case of the relative movement can be, for example, a deviation of the actual movement from the target movement, which can be attributed, for example, to an uneven movement (rattling) of the drives. Further parameters that can be determined are the cutting gap width or the deviation of the cutting gap width from a target cutting gap width, the jet position of a processing nozzle, the deviation of the distance between the (processing) nozzle and the workpiece from a target value, the deviation of the pressure - or gas flow through the nozzle from a desired value, the electrical resistance between the nozzle and the workpiece, and the radiation intensity measured coaxially by means of a sensor in dedicated or predetermined wavelength bands, for example by means of a photodiode in the penetration sensor system. These parameters can be determined in particular in the manner described above in connection with the method.

Further advantages of the invention result from the description and the drawing. Likewise, the features mentioned above and those listed further can be used individually or in combination in any combination. The embodiments shown and described are not to be understood as an exhaustive list, but rather have an exemplary character for the description of the invention.

• 1 eine schematische Darstellung eines Ausführungsbeispiels einer Bearbeitungsmaschine in Form einer Laserbearbeitungsmaschine zum schneidenden Bearbeiten eines Werkstücks,
• 2a,b eine Darstellung eines Laserbearbeitungskopfs der Laserbearbeitungsmaschine von 1, der eine Überwachungseinrichtung aufweist, sowie einer Blende der Überwachungseinrichtung, und
• 3 eine dreidimensionale Darstellung eines Details einer bei dem Laserschneidprozess an einem Werkstück gebildeten Schnittfuge.

Show it:

• 1 1 shows a schematic illustration of an exemplary embodiment of a processing machine in the form of a laser processing machine for cutting processing a workpiece,
• 2a, b a representation of a laser processing head of the laser processing machine of 1 , which has a monitoring device, and an aperture of the monitoring device, and
• 3rd a three-dimensional representation of a detail of a kerf formed on the workpiece in the laser cutting process.

In the following description of the drawings, identical reference numerals are used for identical or functionally identical components.

1 shows a laser processing machine 1 with a laser source 2nd , a laser processing head 4th and a workpiece support 5 . One from the laser source 2nd generated laser beam 6 is by means of a beam guide 3rd with the aid of deflecting mirrors (not shown) to the laser processing head 4th guided and focused in this and with the help of mirrors, also not shown, perpendicular to the surface 8a of a workpiece 8th aligned, ie the beam axis (optical axis) of the laser beam 6 runs perpendicular to the workpiece 8th . In the example shown, the laser source is used 2nd a CO ₂ laser source. Alternatively, the laser beam 6 for example generated by a solid-state laser.

For laser cutting the workpiece 8th is with the laser beam 6 first pierced, ie the workpiece 8th is melted or oxidized at one point and the resulting melt is blown out. Below is the laser beam 6 about the workpiece 8th moves so that a continuous kerf 9 emerges along the laser beam 6 the workpiece 8th severed.

Both grooving and laser cutting can be supported by adding a gas. As cutting gases 10th oxygen, nitrogen, compressed air and / or application-specific gases can be used. Particles and gases can be removed using a suction device 11 from a suction chamber 12th be sucked off.

The laser processing machine 1 also includes a moving device 13 for moving the laser processing head 4th and the workpiece 8th relative to each other. In the example shown, the workpiece is at rest 8th during machining on the workpiece support 5 and the laser machining head 4th is moved during machining along two axes X, Y of an XYZ coordinate system. For this purpose, the movement device 13 a portal displaceable in the X direction with the aid of a drive indicated by a double arrow 14 on. The laser processing head 4th can with the help of another drive indicated by a double arrow of the movement device 13 can be moved in the X direction to any machining position B _{X, Y} in the X direction and in the Y direction in one due to the displaceability of the laser processing head 4th or through the workpiece 8th given working area to be moved. At a respective processing position B _{X, Y} points the laser beam 6 an (instantaneous) machining direction B _φ , which is described by a processing angle φ, which is measured (arbitrarily) starting from the negative Y direction and at which in 1 example shown is φ = 0 °.

As in 2a can be seen, the laser beam 6 for performing cutting work on the workpiece 8th by means of a focusing device in the form of a focusing lens 15 on the workpiece 8th focused. With the focusing lens 15 In the example shown, a lens made of zinc selenide is used to hold the laser beam 6 through a laser machining nozzle 16 , more precisely through their nozzle opening 16a , on the workpiece 8th focused, in the example shown on a focus position F at the top 8a of the workpiece 8th . The laser beam 6 forms an interaction area there 17th with the workpiece 8th , behind the opposite of the machining direction B _φ or contrary to the cutting direction of the laser cutting process the in 1 shown kerf 9 is produced. In the case of a laser beam 6 a focusing lens made of quartz glass, for example, can be used from a solid-state laser.

In 2nd a partially transparent deflection mirror can also be seen 18th which is the incident laser beam 2nd (for example with a wavelength of approx. 10.6 µm) reflected and observation radiation relevant for process monitoring to a further partially transparent deflection mirror 19th transmitted. The deflecting mirror 18th is in the example shown for observation radiation in the form of heat radiation at wavelengths λ from approx. 700 nm to 2000 nm partially transparent. The further partially permeable deflecting mirror 19th reflects the observation radiation to a monitoring device 20th . A source of lighting 21 is used for coaxial illumination of the workpiece 8th with illuminating radiation 22 . The illuminating radiation 22 is from the further partially transmissive deflecting mirror 19th as well as from the deflecting mirror 18th transmitted and through the nozzle opening 16a the laser processing nozzle 16 through to the workpiece 8th directed.

As an alternative to the semi-transparent deflecting mirrors 18th , 19th Scraper mirrors or perforated mirrors, which only reflect incident radiation from an edge area, can also be used to monitor the observation radiation of the monitoring device 20th to supply or around the illuminating radiation 22 the workpiece 8th feed. Also at least one laterally in the beam path of the laser beam 6 inserted mirror can be used to enable observation.

As a lighting source 21 diode lasers or LEDs or flash lamps can be provided, as in 2a shown coaxial, but also off-axis to the laser beam axis 24th can be arranged. The lighting source 21 can for example also outside (in particular next to) the laser processing head 4th arranged and on the workpiece 8th be directed; alternatively, the lighting source 21 inside the laser machining head 4th arranged, but not coaxial to the laser beam 6 on the workpiece 8th be aligned. If necessary, the laser processing head 4th even without a lighting source 21 operate.

Part of the monitoring facility 20th is one in the observation beam path 23 behind the other partially permeable deflecting mirror 19th Arranged geometrically high resolution camera 25th . At the camera 25th can be a high-speed camera that is coaxial to the laser beam axis 24th or to extend the laser beam axis 24th and is thus arranged independent of direction. In the example shown, pictures are taken by the camera 25th in the incident light process in the NIR / IR wavelength range to record the process's own lighting or a thermal image of the cutting process. At the in 2a The example shown can be a filter in front of the camera 25th be arranged if further radiation or wavelength components from the detection with the camera 25th should be excluded. The filter can be designed, for example, as a narrow-band bandpass filter with a half-value width of, for example, approximately 15 nm, the wavelengths λ transmitted in the range around 800 nm.

To generate images of an in 3rd shown area to be monitored 26 of the workpiece 8th which of the kerf 9 or a section of the kerf 9 with the cutting front 9a contains, on a detector surface 25a the camera 25th instructs the monitoring device 20th an imaging optics 27 on. In the example shown, the imaging optics 27 an aperture 28 on that around a central axis of rotation D is rotatably mounted, so that the position of an eccentrically arranged aperture opening during rotation 28a on a circular arc around the axis of rotation D moved (cf. 2 B) .

Due to the arrangement of the panel 28 in which by means of a lens 29 focused beam path of the imaging optics 27 only part of the observation beam path occurs 23 , which has an edge region of the focusing lens 15 passes through and in the convergent beam path after the focusing lens 15 at an angle β to the beam axis 24th of the laser beam 6 is aligned by the eccentric to extend the beam axis 24th of the laser beam 6 arranged aperture 28a and forms an observation beam 23a which is on the detector surface 25a is mapped. At the in 2a shown example runs an observation direction R1 of the observation beam 23a in the projection in the XY plane or in the workpiece plane parallel to the machining direction B _φ (here: φ = 0), along which the laser beam 6 and the workpiece 8th are moved relative to one another in the XY plane in order to form the desired cutting contour, that is to say a sharp observation takes place. The angle β under which the direction of observation R1 to the beam axis 24th of the laser beam 6 in the example shown is between approximately 1 ° and approximately 5 °, for example approximately 4 °.

As in 2a can be seen is on the bezel 28 a polarizing filter 30th attached, which is together with the aperture 28 about the axis of rotation D turns. The polarization filter 30th is designed to filter a linear polarization component p, which in the example shown is aligned parallel to a plane (XZ plane) which represents the (current) machining direction B _φ as well as the Z direction or the beam axis 24th of the laser beam 6 contains. As in 2a can be seen, the observation beam points 23a after the polarization filter 30th only one polarization component aligned perpendicular to the XZ plane s on. The filtering of a linear polarization component of the observation beam 23a has opted for observation of the kerf 9 or the area to be monitored 26 proven to be cheap. It goes without saying that, instead of the polarization component p aligned parallel to the XZ plane, the polarization component aligned perpendicular to the XZ plane may also be used s or a differently oriented polarization component using the polarization filter 30th can be filtered. The use of the s-polarized polarization component has been used to observe the kerf 9 proved to be particularly favorable since the in 3rd shown in dashed lines, which are essentially two light strips 31a , b correspond to have an optimal angle in order to emit a lot of s-polarized radiation.

Instead of a mechanically adjustable cover 28 an electrically adjustable diaphragm, for example in the form of an LCD array, can also be used, in which individual pixels or pixel groups are electronically switched on or off in order to produce the diaphragm effect. The mechanical cover can also be used 28 different from in 2a, b shown across the observation beam path 23 , for example in the YZ plane, are moved or shifted around different parts of the observation beam path 23 shade or open for observation. The aperture 28 can also be realized in the form of one or more mechanical elements that can be opened and closed. The polarization filter can accordingly 30th be designed as an LCD polarizer to suitably choose the orientation of the filtered polarization component, in particular to rotate the orientation of the filtered polarization component. If necessary, the aperture 28 and / or the polarization filter 30th completely from the observation beam path 23 be removed if this is advantageous for monitoring the laser cutting process.

With the help of a monitoring device 20th evaluation device connected in terms of signal technology 32 different parameters for the process quality of the laser cutting process can be determined. For example, based on the course of the in 3rd shown light strips 32a , b on the course of the gap width b (z) of the kerf 9 in the thickness direction Z of the workpiece 8th (with thickness d), more precisely on an angle γ between the two side cut edges 33a , b the kerf 9 getting closed. As parameters for the angle γ can the distance and / or the angle between the two light strips 31a , b using the evaluation device 32 be determined, for example like this in the above WO2018069291A1 which is incorporated by reference in its entirety into the content of this application. The opening angle γ between the two cutting edges 33a , b the kerf 9 represents a parameter for the process quality or for the process robustness typically during fusion cutting, ie the larger the opening angle γ the stronger the V-shape of the kerf 9 pronounced and the worse the cutting quality is typically.

As in 3rd can also be seen, is formed during the cutting process on the workpiece 8th at the front edge of the kerf 9 the essentially cylindrical cutting front 9a made up along the thickness d of the workpiece 8th at a cutting front angle α regarding the top 8a and the bottom 8b of the workpiece 8th extends. With the help of the monitoring device 20th can be based on the monitored area 26 , more precisely based on the interaction area 17th , with the help of the evaluation device 32 the cutting front angle α be determined. This can be done, for example, in a manner such as that cited in the introduction WO2015036140A1 which is incorporated by reference in its entirety into the content of this application. In this case it is for the determination of the cutting front angle α favorable when observing the interaction area 17th with a sluggish or piercing observation direction, with the use of the polarization filter 30th can be dispensed with. Alternatively, the cutting front angle α also based on the geometry of the kerf 9 can be determined, for example as this in the above WO2012107331A1 is described, which is also made by reference in its entirety to the content of this application.

With the help of the monitoring device 20th or the evaluation device 32 can also use other parameters for process quality, such as positioning accuracy P _{X, Y} when positioning the laser processing head 4th at the processing position B _{X, Y} , ie the deviation between the actual and target processing position and the directional accuracy R _φ , ie the deviation of the current machining direction B _φ at the processing position B _{X, Y} be determined from a target machining direction. The directional inaccuracy R _φ can from the monitoring device 20th in combination with the evaluation device 32 can also be determined, for example, by using the DE102005022095A1 described method for determining the lateral relative movement between the laser processing head 4th and the workpiece 8th is carried out and the lateral relative movement or current machining direction determined in this way B _φ is compared with a value for the target machining direction, that in the evaluation device 32 or is stored in another location. The position accuracy P _{X, Y} as well as the directional accuracy R _φ represent parameters for the process quality, as there are deviations in the geometry of the kerf in the event of deviations from the respective setpoint 9 comes from a target geometry.

It is understood that with the help of the monitoring device 20th or the evaluation device 32 other parameters for the process quality can also be determined, for example the occurrence of burrs at the kerf 9 etc. concern, as also in the WO2012107331A1 is described. The type of parameter (s) for the process quality used in the evaluation device 32 can be determined can depend on the type of laser cutting process, for example the cutting front angle α serve as a parameter in a flame cutting process, during the opening angle γ the kerf typically serves as a parameter for the process quality in a fusion cutting process.

One in 1 shown control device 34 , the control tasks of the laser cutting machine 1 takes over, stands with the evaluation device 32 in signaling connection. The control device 34 has a control device 35 to generate optimal process quality in the machining process. The control device 35 can be designed, for example, the cutting front angle α to regulate to a predetermined, constant value by at least one control parameter, for example the feed rate and / or the power of the laser beam 6 is suitably influenced.

The following is an example of the cutting front angle α as a parameter for the Process quality is described, such as position and / or direction-dependent malfunctions when machining the workpiece 8th by means of the processing machine 1 be determined. As described above, the cutting front angle α continuously from the monitoring device during the cutting process 20th detected. A respective instantaneously determined measured value of the cutting front angle α becomes the current machining position B _{X, Y} assigned, in the example shown an XY coordinate in the working area of the processing machine 1 corresponds. The assignment can be stored, for example, in a database or the like, which is stored in the evaluation device 32 , the control device 34 or in a data store 36 is stored, which may be provided on an external, central computer or in the cloud. The assignment of the cutting front angle α to the respective processing positions B _{X, Y} in the work area is for a number of cutting machining processes and thus for a number of measurement values α ₁ , α ₂ , ... α _N made, where N describes the number of measured values, which is typically more than N = 10. From the measured values α ₁ , α ₂ , ... α _N that at a respective processing position B _{X, Y} , that is, at a respective XY coordinate in the working area, a cutting front angle dependent on the XY coordinate or the XY position in the working area becomes α (X, Y) determined. The position-dependent cutting front angle α (X, Y) is therefore a function depending on the XY coordinate.

The influence of the respective machining process or the respective machining parameters on the position-dependent cutting front angle α (X, Y) to eliminate is a statistical analysis of the plurality N of measured values α ₁ , α ₂ , ... α _N carried out at different times or with different machining processes at the respective machining position B _{X, Y} were determined. In the simplest case, the position-dependent cutting front angle can be determined α (X, Y) the average of the measured values α ₁ , α ₂ , ... α _N at the respective processing position B _{X, Y} be calculated. It goes without saying that, instead of the mean value, another suitable statistical measure for determining the position-dependent cutting front angle α (X, Y) can be used, which is the influence of disturbances that are not of the respective processing position B _{X, Y} dependent are eliminated as completely as possible.

Based on the position-dependent cutting front angle α (X, Y) in the work area, processing positions B _{X, Y} can be determined at which the position-dependent cutting front angle α (X, Y) is so small that the process quality is low or the process may no longer be stable. To these machining positions B _{X, Y} can determine the position-dependent cutting front angle α (X, Y) can be compared with a (usually constant, ie not dependent on position) threshold value. The processing positions B _{X, Y} , at which the threshold value is undershot, form partial areas in the form of fault position areas 37 within the work field, of which two are exemplary 1 are shown. The subareas of the work area that are outside the fault position areas 37 lie, form preferred position areas for the cutting process on the workpiece 8th .

During path planning in the control system 34 the cutting contours to be generated during cutting are those from the workpiece 8th Workpiece parts to be cut are selected so that they ideally completely outside the fault position areas 37 or that the smallest possible part of the machining process is within the fault position areas 37 he follows. The fault position ranges determined in the manner described above 37 the processing machine 1 can in the data store 36 can be saved.

The determination of the fault position areas 37 in the manner described above, repetitions can optionally be made at predetermined time intervals. Used to determine the position-dependent cutting front angle α a sufficiently large one Number of measurements α ₁ , α ₂ , ... α _N used, the fault position ranges change 37 generally not or only insignificantly, ie these are essentially constant over time. The information about the fault position areas 37 a variety of processing machines 1 same design can be in a common data storage 36 get saved. Based on the data stored there about the fault position areas 37 and / or via the position-dependent cutting front angle α (x, y) weaknesses in the machine design can be identified.

Analogous to the determination of the position-dependent cutting front angle described above α (X, Y) can the cutting front angle α also depending on the machining direction B _φ be determined. In the simplest case, a measured value for the cutting front angle is determined at the moment α a respective current machining direction B _φ - without taking into account the respective machining position B _{X, Y} - assigned, ie it becomes the direction-dependent cutting front angle α _φ the processing machine 1 regardless of the processing position B _{X, Y} determined by a plurality of measured values for the direction-dependent cutting front angle α _φ is statistically evaluated in the manner described above. The direction-dependent cutting front angle is preferred α _φ but also depending on the processing position B _{X, Y} determined, ie the direction-dependent cutting front angle α _φ is based on a plurality of measured values α ₁ , α ₂ , ... α _N in a respective processing direction B _φ at one and the same processing position B _{X, Y} determined. The directional cutting front angle α _φ (X, Y) is therefore also dependent on the XY position in the work area.

Analogous to the determination of the fault position ranges described above 37 can also be interference angle ranges 38 can be determined, possibly from the respective processing position B _{X, Y} are dependent ( s .O.). For example, the respective value for the direction-dependent cutting front angle can be used for this purpose α _φ can be compared with a threshold. In 1 is an example of a disturbance angle range 38 at a processing position B _{X, Y} shown, which extends over an angular interval φ between approximately 35 ° and approximately 45 °. As above in connection with the fault position areas 37 the machining directions can also be described B _φ when machining the workpiece 8th be chosen so that the interference angle ranges 38 should be avoided when processing. The direction-dependent, typically additionally position-dependent cutting front angle α _φ (X, Y) or the interference angle ranges 38 can also in the data store 36 be saved in order to be able to carry out a fault diagnosis or to optimize work planning.

As described above, the cutting front angle can α can be regulated to a predetermined, constant value by at least one control parameter, for example the feed rate and / or the power of the laser beam 6 is suitably influenced. In the case of an (ideal) control, the controlled variable is constant, ie does not depend on the position and / or the direction, but the measured variable (s) used for the control can vary depending on the position and / or direction due to interference, what should be taken into account in the control, the controlled variable, in the example described here the cutting front angle α to keep constant.

When laser cutting over a web of the workpiece support 5 For example, a high measurement signal from an optical laser cutting sensor system can result, which detects the process radiation as a measurement variable. At such a processing position B _{X, Y} Therefore, it must either not be controlled at all or a high value of the measured variable must be expected to match the controlled variable, for example the cutting front angle α to keep constant. In this case, the measurement signal of the process radiation is a position-dependent parameter, which is determined with the aid of the method described above, and that of the processing position B _{X, Y} dependent variation is taken into account when regulating the controlled variable to its target value. It goes without saying that such a procedure is also possible for other parameters.

When laser cutting with a laser beam 6 with an oval beam cross-section, for example due to a non-circular inner contour 16a the nozzle 16 can be used for regulating the cutting gap 9 to a constant width b (controlled variable), for example the focus position F of the laser beam 6 in the direction of propagation of the laser beam 6 (in the Z direction) can be adjusted as a manipulated variable. You cut with the long side of the laser beam 6 across the cutting gap 9 , the focus position F be chosen so that the beam cross section of the laser beam 6 on the workpiece 9 is small, while when cutting with the narrow laser beam side across the cutting gap 9 the beam cross-section in the focus should be set large, so that overall the width b of the cutting gap 9 can be kept constant. In this case, a direction-dependent adjustment of the focus position or the focus position in the Z direction is required.

With increasing operating time of the laser processing machine 1 for example, the focusing lens may become dirty 15 come. The contamination can lead to a so-called thermal lens, which changes the focus position F (Deviation from a nominal focus position). Becomes the focus position F (in the direction of propagation) of the laser beam 6 as a parameter for several machining processes in succession on the laser processing machine 1 determined, it may therefore be useful to change the measured values over time when determining the directional and / or position-dependent focus position F to consider. For example, when determining the focus position F only those measured values are taken into account that were determined in machining processes not long ago and therefore the current degree of contamination of the focusing lens 15 correspond.

It is understood that the method described above in an analogous manner also with parameters for the process quality other than the cutting front angle α , the focus position F , etc. can be carried out.

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• WO 2012107331 A1 [0002, 0024, 0049, 0051]
• WO 2015036140 A1 [0003, 0024, 0049]
• WO 2018069291 A1 [0004, 0024, 0048]
• DE 102005022095 A1 [0005, 0015, 0025, 0050]
• EP 3159093 A1 [0006]
• DE 102011079083 A1 [0007]
• EP 1497851 [0008]

Claims (16)

Method for determining at least one parameter (α, γ, P _{X, Y} , R _φ ) for the process quality in a machining process, in particular in a laser cutting process, comprising: in particular cutting machining of a workpiece (8) while moving a machining tool, in particular a laser machining head ( 4), and the workpiece (8) relative to one another, monitoring an area (26) on the workpiece (8), which preferably comprises an interaction area (17) of the processing tool, in particular the laser processing head (4), with the workpiece (8), and determining at least one parameter (α, γ, P _{X, Y} , R _φ ) for the process quality based on the monitored area (26), characterized by determining at least one position-dependent parameter (α (x, y)) for the process quality based on a plurality of measured values (α ₁ , ... α _N ) of the at least one parameter (a) at the same processing position (B _{X, Y} ) and / or at least one he direction-dependent parameter (α _φ , α _φ (x, y)) for the process quality based on a plurality of measured values (α ₁ , ... α _N ) of the at least one parameter (α) in the same machining direction (B _φ ), in particular in same machining direction (B _φ ) at one and the same machining position (B _{X, Y} ). Procedure according to Claim 1 , in order to determine the position-dependent parameter (a (x, y)) and / or the direction-dependent parameter (α _φ , α _φ (x, y)) for the process quality, a statistical analysis of the plurality of measured values (α ₁ , .. . α _N ) is carried out. Method according to one of the preceding claims, in which the parameter (a) is recorded continuously during a machining process and a currently determined measured value of the parameter (a) is assigned to a respective machining position (B _{X, Y} ) and / or a respective machining direction (B _φ ) becomes. Method according to one of the preceding claims, in which machining positions (B _{X, Y} ) are determined on the basis of the position-dependent parameter (a (x, y)), which form at least one fault position region (37) during machining and / or on the basis of the direction-dependent one Characteristic (α _φ , α _φ (x, y)) machining directions (B _φ ) are determined, which form at least one interference angle range (38) during machining. Method according to one of the preceding claims, in which machining positions (B _{X, Y} ) and / or machining directions (B _φ ) during the movement of the machining tool and the workpiece (8) relative to one another as a function of the determined position-dependent parameter (a (x, y )), in particular from the interference position range (37), and / or on the basis of the direction-dependent parameter (α _φ , α _φ (x, y)), in particular from the interference angle range (38). Method according to one of the preceding claims, in which the plurality of measured values (α ₁ , ... α _N ) of the at least one parameter (a) is determined in the case of several machining processes on the same machine tool (1) and / or the position-dependent parameter (a ( x, y)) and / or the direction-dependent parameter (α _φ , α _φ (x, y)) is / are determined on several identical processing machines (1). Procedure according to Claim 6 , in which the majority of the measured values (α ₁ , ... α _N ) of the at least one parameter (a) is determined in several machining processes on the same processing machine (1) and in which the position-dependent parameter (a (x, y) ) and / or the direction-dependent parameter (α _φ , α _φ (x, y)) a temporal change in the measured values (α ₁ , ... α _N ) is taken into account. Method according to one of the preceding claims, further comprising: storing the determined position-dependent parameter (a (x, y)) and / or the fault position range (37) and / or the determined direction-dependent parameter (α _φ , α _φ (x, y)) and / or the interference angle range (38) in a data memory (36). Method according to one of the preceding claims, in which the parameter is selected from the group comprising: cutting front angle (a) a cutting front (9a) of a kerf (9) and opening angle (γ) between two cutting edges (33a, b) of the kerf ( 9). Method according to one of the preceding claims, in which the parameter is selected from the group comprising: positioning accuracy (P _{X, Y} ) and directional accuracy (R _φ ) when moving the machining tool and the workpiece (8) relative to one another. Processing machine, in particular laser processing machine (1), comprising: a processing tool, in particular a laser processing head (4), for in particular cutting processing of a workpiece (8), a movement device (13) for moving the processing tool and the workpiece (8) relative to one another, and a Monitoring device (20) for monitoring an area (26) on the workpiece (8), which preferably an interaction area (17) of the machining tool, in particular the Laser processing head (4), with the workpiece (8), and an evaluation device (32), which is configured based on the monitored area (26) at least one parameter (α, γ, P _{X, Y} , R _φ ) for the process quality to be determined, characterized in that the evaluation device (32) is configured to determine at least one position-dependent parameter (a (x, y)) for the process quality on the basis of a plurality of measured values (α ₁ , ... α _N ) of the at least one parameter ( a) at the same processing position (B _{X, Y} ) and / or at least one direction-dependent parameter (α _φ , a _φ ) (x, y)) for the process quality on the basis of a plurality of measured values (α ₁ , ... α _N ) to determine at least one parameter (a) along the same machining direction (B _φ ), in particular along the same machining direction (B _φ ) at one and the same machining position (B _{X, Y} ). Processing machine after Claim 11 , in which the evaluation device (32) is configured, for determining the position-dependent parameter (a (x, y)) and / or the direction-dependent parameter (α _φ , α _φ (x, y)) for the process quality, a statistical analysis of the plurality of measured values (α ₁ , ... α _N ). Processing machine after Claim 11 or 12th , in which the monitoring device (20) is designed to continuously monitor the at least one parameter (a) and in which the evaluation device (32) is designed, a momentarily determined measured value of the parameter (a) of a respective processing position (B _{X, Y} ) and / or to assign a respective machining direction (B _φ ). Processing machine according to one of the Claims 11 to 13 , in which the evaluation device (32) is configured to use the position-dependent parameter (α (x, y)) to determine machining positions (B _{X, Y} ) which form at least one fault position region (37) during machining and / or using the direction-dependent one Determine characteristic (α _φ , α _φ (x, y)) machining directions (B _φ ) which form at least one interference angle range (38) during machining. Processing machine according to one of the Claims 11 to 14 , further comprising: a control device (35) for controlling the movement of the machining tool and the workpiece (8) relative to one another, which is preferably configured, machining positions (B (x, y)) and / or machining directions (B (φ)) in the Movement of the machining tool and the workpiece (8) relative to one another as a function of the determined position-dependent parameter (a (x, y)), in particular of the fault position range (37), and / or using the direction-dependent parameter (α _φ , α _φ (x , y)), in particular of the interference angle range (38). Processing machine according to one of the Claims 11 to 15 , in which the monitoring device (20) and the evaluation device (32) are configured, using the monitored area (26) as a parameter for the process quality, a cutting front angle (a) a cutting front (9a) of a kerf (9), an opening angle ( γ) between two cutting edges (33a, b) of the kerf (9) to determine a positioning accuracy (P _{X, Y} ) and / or a directional accuracy (R _φ ) when moving the processing tool and the workpiece (8) relative to each other.

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